The invention pertains to a polycrystalline diamond member, and in particular, to a polycrystalline diamond member having a backing of polycrystalline diamond and a layer of a hard chemical vapor deposition (CVD) coating, i.e., a hard material applied by CVD techniques, on the backing.
Heretofore, a typical polycrystalline diamond compact comprises a backing of tungsten carbide (or cobalt cemented tungsten carbide) and a polycrystalline diamond layer on the backing. The polycrystalline diamond layer comprises diamond particles bridged together (i.e., bonded together by bridging) with a catalyst (e.g., cobalt) at the interstices of the diamond particles. The cobalt acts as a catalyst for the bridging together of the diamond particles. Such a polycrystalline diamond compact is shown and described in U.S. Pat. No. 4,604,106 to Hall et al. for a COMPOSITE POLYCRYSTALLINE DIAMOND COMPACT, wherein the Hall et al. patent is hereby incorporated by reference herein. Although it depends upon the specific application for use, in the case of use as a polycrystalline diamond (PCD) blank for a PCD cutting insert, these polycrystalline diamond compacts are cut into sections and then polished to some extent to form a PCD blank whereby the PCD blank is then brazed into a pocket in a substrate for the PCD cutting insert. The PCD blank has a rake surface and flank surfaces which intersect to define the cutting edges of the PCD cutting insert. The typical PCD blank has a catalyst (e.g., cobalt) content between about 5 weight percent and about 6 weight percent and the average particle size of the diamond particles varies depending upon the application. The broader range for the average particle size of the diamond particles may be between about 2 micrometers (xcexcm) and about 25 xcexcm with other ranges of between about 2 xcexcm and about 10 xcexcm and between about 10 xcexcm and about 25 xcexcm.
In a co-pending U.S. patent application by E. J. Oles and L. E. Thomas entitled CUTTING INSERT WITH IMPROVED FLANK SURFACE ROUGHNESS AND METHOD OF MAKING, which is hereby incorporated by reference herein, and assigned to the assignee (Kennametal Inc. of Latrobe, Pa. 15650, USA) of this patent application, there is disclosed a PCD cutting insert which includes a PCD blank. The PCD blank has a rake surface that has been roughened using ion milling, laser or plasma etching so as to achieve a surface roughness sufficient to provide for microscopic chip control during a material removal process. The PCD blank has been finish-ground so that on the flank surfaces there are the finish-grind lines therein which lie in a direction that is generally parallel to the cutting edges, and the flank surfaces have been polished so that they have a mirror finish (less than 5 microinches, Ra). Such a PCD cutting insert provides for microscopic chip control due to the roughened rake surface and also provides a workpiece surface finish that approaches theoretical values due to the smoothness of the flank surfaces.
While the above-described earlier PCD cutting insert provides certain advantages and it is a very satisfactory PCD cutting insert, certain aspects for improvement still remain.
In the above-described earlier PCD cutting insert, the surface which contacts the workpiece during the material removal process is not especially made for contacting the workpiece surface. In other words, the microstructure of the diamond layer of the earlier PCD blank is generally consistent throughout. It would be highly desirable to provide a PCD cutting insert that has a PCD blank with a surface which contacts the workpiece that has been especially made to accommodate such contact, and wherein the PCD blank also provides for microscopic chip control and a workpiece surface finish that approaches theoretical values.
In the above-described earlier PCD cutting insert, the rake surface achieves its roughness through a separate roughening step such as ion milling, plasma etching or laser blading. It would be highly desirable to provide a PCD cutting insert with a PCD blank with a roughened rake surface wherein the roughness is not formed by a separate processing step, and wherein the PCD blank also provides for microscopic chip control and a workpiece surface finish that approaches theoretical values.
In one form thereof, the invention is a polycrystalline diamond member which includes a backing, and a layer of polycrystalline diamond on the backing wherein the layer of polycrystalline diamond has a rake surface and a flank surface. The layer of polycrystalline diamond has an interior region adjacent to the backing and an exterior region adjacent to the interior region wherein the exterior region terminates at the rake surface. The interior region comprises interior diamond particles and a catalyst wherein the interior diamond particles are bridged together so as to form interstices therebetween, and the catalyst is at the interstices of the interior diamond particles. The exterior region comprises exterior diamond particles bridged together so as to form interstices therebetween and the exterior region is essentially free of the catalyst. A chemical vapor deposition-applied hard material essentially surrounds the exterior diamond particles.
In another form thereof, the invention is a polycrystalline diamond cutting insert which comprises a substrate that contains a pocket therein. A polycrystalline diamond blank has a backing and a layer of polycrystalline diamond on the backing. The layer of polycrystalline diamond has an interior region adjacent to the backing and an exterior region adjacent to the interior region. The interior region comprises interior diamond particles and a catalyst wherein the interior diamond particles are bridged together so as to form interstices therebetween. The catalyst is at the interstices of the interior diamond particles. The exterior region comprises exterior diamond particles bridged together so as to form interstices therebetween and the exterior region is essentially free of the catalyst. A chemical vapor deposition-applied hard material essentially surrounds the exterior diamond particles.
In still another form thereof, the invention is a method of making a polycrystalline diamond member comprising the steps of: providing a backing; providing a polycrystalline diamond layer on the backing wherein the polycrystalline diamond comprises a plurality of diamond particles and a catalyst with the diamond particles being bridged together so as to form interstices therebetween and the catalyst being at the interstices of the diamond particles; removing the catalyst from the polycrystalline diamond layer beginning at a portion of the surface of the polycrystalline diamond layer to a predetermined depth so as to form: an exterior region comprising exterior ones of the diamond particles bridged together so as to form interstices therebetween, and the exterior region being essentially free of the catalyst, and an interior region inwardly of the exterior region, and the interior region comprising interior ones of the diamond particles and a catalyst, and the interior diamond particles being bridged together so as to form interstices therebetween, and the catalyst being at the interstices of the interior diamond particles; and depositing beginning at the portion of the surface of the polycrystalline diamond layer a volume of hard material whereby the rate of deposition is sufficiently slow so as to permit the hard material to infiltrate between the bridged-together exterior diamond particles so as to essentially surround the exterior diamond particles whereby the exterior region comprises exterior diamond particles bridged together with the hard material essentially surrounding the exterior diamond particles.
In yet another form thereof, the invention is a method of making a polycrystalline diamond cutting insert comprising the steps of: providing a substrate having a pocket therein; providing a polycrystalline diamond blank having a backing with a polycrystalline diamond layer on the backing wherein the polycrystalline diamond layer has a rake surface and a flank surface which intersect to form a cutting edge, and the polycrystalline diamond layer comprises a plurality of diamond particles and a catalyst with the diamond particles being bridged together so as to form interstices therebetween and the catalyst being at the interstices between the diamond particles; removing the catalyst from the polycrystalline diamond layer beginning at a portion of the surface of the polycrystalline diamond layer to a predetermined depth so as to form: an exterior region comprising exterior ones of the diamond particles bridged together so as to form interstices therebetween, and the exterior region being essentially free of the catalyst, and an interior region inwardly of the exterior region and the interior region comprising interior ones of the diamond particles being bridged together so as to from interstices therebetween and the catalyst, and the catalyst being at the interstices between the interior diamond particles; depositing beginning at the portion of the surface of the polycrystalline diamond layer a volume of hard material whereby the rate of deposition is sufficiently slow so as to permit the hard material to infiltrate between the bridged-together exterior diamond particles whereby the exterior region comprises the exterior diamond particles bridged together with the hard material essentially surrounding the exterior diamond particles; brazing the polycrystalline blank into the pocket; and finish-grinding the flank surface of the polycrystalline diamond layer so that the finish-grind lines lie in a direction generally parallel to the cutting edge.